This invention relates to a process for etching Fe-containing materials to be used as the magnetic poles in thin-film magnetic heads and magnetic sensors and to an apparatus therefor.
Ion milling by an argon ion beam etching apparatus has conventionally been used for etching Fe-containing materials. In this process, which can be referred to as a physical etching, a solid sample is subjected to ion bombardment of an ionized inert gas such as an argon gas accelerated under application of electric field, and the sputtering phenomenon occurring at the surface of the sample is utilized for etching. The conditions for the ion milling using argon gas are usually set as follows: argon gas pressure -4.times.10.sup.-4 torr, ion accelerating voltage=450 V, ion current density=0.6 mA/cm.sup.2, and ion beam incident angle=0.degree. to 45.degree.. The etching rate achievable by ion milling is about 100 to 150 A/min in the case of Fe-Si-Al alloys or pure Fe, and about 200 to 250 A in the case of Ni-Zn-Fe.sub.2 O.sub.4 (ferrite).
The argon ion milling of the above techniques for etching Fe-containing materials suffers a problem of etching selectivity, i.e. there is a difference between the etching rate of PR (photoresist) and that of the material to be etched, since it is a physical etching and photoresists are also etched together with the materials. For example, the ratio of etching rate of pure Fe to that of PR is about 2:1, which is not sufficient in practical uses. When a 3 .mu.m thick pure Fe material, for example, is to be etched, a PR pattern having vertical side walls and a thickness of at least about 1.5 .mu.m, practically not less than 2 .mu.m taking process margins into consideration, must be formed. However, it has been difficult to form such vertically cut pattern having a rectangular cross section. Beside, the achievable etching rate is about 150 A/min, and it takes 200 minutes to achieve etching of a thickness of, for example, 3 .mu.m, so that the articles obtained by application of prior art have suffered low throughputs, leading to cost elevation. What is more serious is the cross-sectional shape of the etched Fe-containing material. When the argon ion milling process is carried out using a 3 .mu.m wide PR pattern having a rectangular cross section as shown in FIG. 1(A), etching takes place in the Fe-containing material to have a trapezoidal cross section, as shown in FIG. 1(B). Since the cross section of the article etched by the prior art thus comes to have a trapezoidal cross section, the following problems occur when the prior art technique is applied to a process of making a thin-film magnetic head:
(1) The recording track width at the upper part of the thus obtained head and that at the lower part thereof will be greatly different, and the track width, a parameter for deciding the basic characteristics as the magnetic head, cannot accurately be defined;
(2) When a smaller track width is to be formed, the cross section of the upper part of the magnetic pole will be triangular to provide a very narrow track which limits increase in the recording density.
An object of this invention is to provide a process for etching a Fe-containing material which can overcome the above problems and an apparatus therefor.